{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T21:30:44Z","timestamp":1787693444119,"version":"build-2784847793"},"reference-count":48,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2022,3,23]],"date-time":"2022-03-23T00:00:00Z","timestamp":1647993600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002347","name":"Federal Ministry of Education and Research","doi-asserted-by":"publisher","award":["031B0831C"],"award-info":[{"award-number":["031B0831C"]}],"id":[{"id":"10.13039\/501100002347","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002347","name":"Federal Ministry of Education and Research","doi-asserted-by":"publisher","award":["031B0078A"],"award-info":[{"award-number":["031B0078A"]}],"id":[{"id":"10.13039\/501100002347","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Toxins"],"abstract":"<jats:p>Cell-free protein synthesis (CFPS) represents a versatile key technology for the production of toxic proteins. As a cell lysate, rather than viable cells, is used, the toxic effects on the host organism can be circumvented. The open nature of cell-free systems allows for the addition of supplements affecting protein concentration and folding. Here, we present the cell-free synthesis and functional characterization of two AB5 toxins, namely the cholera toxin (Ctx) and the heat-labile enterotoxin (LT), using two eukaryotic cell-free systems based on Chinese hamster ovary (CHO) and Spodoptera frugiperda (Sf21) cells. Through an iterative optimization procedure, the synthesis of the individual AB5 toxins was established, and the formation of multimeric structures could be shown by autoradiography. A functional analysis was performed using cell-based assays, thereby demonstrating that the LT complex induced the characteristic cell elongation of target cells after 24 h. The LT complex induced cell death at higher concentrations, starting at an initial concentration of 5 nM. The initial toxic effects of the Ctx multimer could already be detected at 4 nM. The detection and characterization of such AB5 toxins is of utmost importance, and the monitoring of intracellular trafficking facilitates the further identification of the mechanism of action of these toxins. We showed that the B-subunit of LT (LTB) could be fluorescently labeled using an LTB-Strep fusion protein, which is a proof-of-concept for future Trojan horse applications. Further, we performed a mutational analysis of the CtxA subunit as its template was modified, and an amber stop codon was inserted into CtxA\u2019s active site. Subsequently, a non-canonical amino acid was site-specifically incorporated using bio-orthogonal systems. Finally, a fluorescently labeled CtxA protein was produced using copper-catalyzed click reactions as well as a Staudinger ligation. As expected, the modified Ctx multimer no longer induced toxic effects. In our study, we showed that CFPS could be used to study the active centers of toxins by inserting mutations. Additionally, this methodology can be applied for the design of Trojan horses and targeted toxins, as well as enabling the intracellular trafficking of toxins as a prerequisite for the analysis of the toxin\u2019s mechanism of action.<\/jats:p>","DOI":"10.3390\/toxins14040233","type":"journal-article","created":{"date-parts":[[2022,3,23]],"date-time":"2022-03-23T22:08:06Z","timestamp":1648073286000},"page":"233","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":22,"title":["Cell-Free Systems Enable the Production of AB5 Toxins for Diagnostic Applications"],"prefix":"10.3390","volume":"14","author":[{"given":"Franziska","family":"Ramm","sequence":"first","affiliation":[{"name":"Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am M\u00fchlenberg 13, 14476 Potsdam, Germany"},{"name":"Institute of Chemistry and Biochemistry\u2014Biochemistry, Freie Universit\u00e4t Berlin, Takustr. 6, 14195 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lena","family":"Jack","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am M\u00fchlenberg 13, 14476 Potsdam, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Danny","family":"Kaser","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am M\u00fchlenberg 13, 14476 Potsdam, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeffrey L.","family":"Schlo\u00dfhauer","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am M\u00fchlenberg 13, 14476 Potsdam, Germany"},{"name":"Institute of Chemistry and Biochemistry\u2014Biochemistry, Freie Universit\u00e4t Berlin, Takustr. 6, 14195 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4895-5423","authenticated-orcid":false,"given":"Anne","family":"Zemella","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am M\u00fchlenberg 13, 14476 Potsdam, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stefan","family":"Kubick","sequence":"additional","affiliation":[{"name":"Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am M\u00fchlenberg 13, 14476 Potsdam, Germany"},{"name":"Institute of Chemistry and Biochemistry\u2014Biochemistry, Freie Universit\u00e4t Berlin, Takustr. 6, 14195 Berlin, Germany"},{"name":"Faculty of Health Sciences, Joint Faculty of the Brandenburg University of Technology Cottbus\u2013Senftenberg, Brandenburg Medical School Theodor Fontane and the University of Potsdam, 14476 Potsdam, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,3,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"15562","DOI":"10.1074\/jbc.272.24.15562","article-title":"Proteolytic activation of cholera toxin and Escherichia coli labile toxin by entry into host epithelial cells. 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